Electronic image-movement correcting device with a variable correction step feature

ABSTRACT

An image-shake correcting device includes a motion-vector detecting circuit for detecting a motion vector relative to pictures, an electronic correcting circuit for electronically correcting an image shake on the basis of the motion vector detected by the motion-vector detecting circuit, an image enlarging circuit for performing enlargement processing on an image signal outputted from the electronic correcting circuit, and a control circuit for controlling a correction step of the electronic correcting circuit on-the basis of an image enlargement ratio of the image enlarging circuit to set the correction step to an optimum state.

This application is a division of application Ser. No. 08/904,455, filedAug. 1, 1997, now U.S. Pat. No. 5,825,415.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image-shake correcting device forpreventing an image picked up by an image pickup apparatus from beingshaken by a vibration of a hand or the like and, more particularly, toan image-shake correcting device suitable for use in an image pickupapparatus, such as a portable video camera.

2. Description of the Related Art

It is known that, in an image pickup apparatus such as a video camera,whether the industrial or domestic type, a vibration of the cameravisually impairs an image and causes various kinds of malfunctions. Itis also known that an image shake easily occurs particularly whenphotography is performed during walking, in a vehicle which is running,or in a place which vibrates to a significant extent. For these reasons,to correct such an image shake, it has heretofore been proposed toprovide various types of image-shake correcting devices which will bedescribed below.

For example, an inertial pendulum type of image-shake correcting device(U.S. Pat. Nos. 2,959,088 and 2,829,557 and the like) is known. In theinertial pendulum type of image-shake preventing device, an inertialpendulum type of shake preventing lens having a two-axes gimbalstructure is disposed around a master lens, and an image shake iscancelled by this shake preventing lens, thereby correcting the imageshake. Another example is a variable-angle-prism type of image-shakecorrecting device in which a variable angle prism for varying theoptical axis of a lens (front lens) is disposed in front of the lens,and which is arranged to detect a movement from an image signaloutputted from an image pickup element (CCD) or to detect a movement bymeans of an acceleration sensor, and drive the variable angle prism onthe basis of the resultant detection signal, thereby correcting an imageshake. Yet another example is a purely electronic image-shake correctingdevice which is arranged to store a video signal outputted from an imagepickup element (CCD) in an image memory or the like, detect an imageshake from information about the video signal to find the amount ofdisplacement of the image, and shift an image reading address of theimage memory according to the amount of displacement of the image,thereby correcting the image shake (Japanese Laid-Open PatentApplication No. Sho 63-166370).

The third one of the above-described examples, i.e., the purelyelectronic image-shake correcting device, has recently receivedattention. This is because the purely electronic image-shake correctingdevice does not need any special mechanical mechanism for correcting animage shake and can be reduced in size, weight and cost owing to therapid advance of semiconductor technology which makes it possible toaccommodate a large-scale electrical circuit into an extremely smallpackage.

However, the above-described purely electronic image-shake correctingdevice has a number of problems. For example, if an electronicallyenlarged image is corrected by moving (shifting) the electronicallyenlarged image with a correction step of not greater than the minimumpixel of the image pickup element, a moiré noise which leads to an imagedegradation may be caused by a movement of a position at which aresolution degradation occurs due to image enlargement processing,although the degree of the moiré noise depends on an image enlargementratio and the kind of image. If an image is not electronically enlargedand is merely moved with the correction step of not greater than theminimum pixel of the image pickup element, a resolution degradationstill occurs and a large image degradation occurs due to image-shakecorrection.

SUMMARY OF THE INVENTION

A first object of the present invention which has been made in light ofthe above-described problems is to provide an electronic image-shakecorrecting device which causes no large image degradation.

A second object of the present invention is to provide an image-shakecorrecting device capable of minimizing a resolution degradation and amoiré noise due to a movement of the position of occurrence of theresolution degradation, thereby minimizing an image degradation due toimage-shake correction.

To achieve the above-described objects, according to one aspect of thepresent invention, there is provided an image pickup apparatus whichcomprises motion-vector detecting means for detecting a motion vectorrelative to images, electronic correcting means for electronicallycorrecting an image shake on the basis of the motion vector detected bythe motion-vector detecting means, image enlarging means for performingimage enlargement processing on a picked-up image signal whose imageshake is corrected by the electronic correcting means,image-enlargement-ratio varying means for varying an image enlargementratio of the image enlarging means, and control means for controlling acorrection step of the electronic correcting means in accordance withthe image enlargement ratio set by the image-enlargement-ratio varyingmeans to set the correction step to an optimum state.

To achieve the above-described objects, according to another aspect ofthe present invention, there is provided an image pickup apparatus whichcomprises image pickup means, motion-vector detecting means fordetecting a motion vector relative to images, absolute-deviationcomputing means for computing an absolute deviation from a referencepoint of a current image on the basis of the motion vector detected bythe motion-vector detecting means, electronic correcting means forelectronically correcting an image shake on the basis of the absolutedeviation computed by the absolute-deviation computing means, detectingmeans for detecting whether the image pickup means is fixed, and controlmeans for controlling a correction step of the electronic correctingmeans on the basis of a detection signal provided by the detecting meansto set the correction step to an optimum state.

To achieve the above-described objects, according to yet another aspectof the present invention, there is provided an image pickup apparatuswhich comprises motion-vector detecting means for detecting a motionvector relative to images, absolute-deviation computing means forcomputing an absolute deviation from a reference point of a currentimage on the basis of the motion vector detected by the motion-vectordetecting means, electronic correcting means for electronicallycorrecting an image shake on the basis of the absolute deviationcomputed by the absolute-deviation computing means, zoom magnificationdetecting means for detecting a zoom magnification, and control meansfor controlling a correction step of the electronic correcting meansaccording to the zoom magnification detected by the zoom magnificationdetecting means to set the correction step to an optimum state.

The above and other objects, features and advantages of the presentinvention will become apparent from the following detailed descriptionof preferred embodiments of the present invention, taken in conjunctionwith the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing the arrangement of a video camerawhich is an image pickup apparatus provided with an image-shakecorrecting device according to a first embodiment of the presentinvention;

FIG. 2 is a flowchart showing the control operation of a logic operationcircuit provided in the image-shake correcting device shown in FIG. 1;

FIG. 3 is a view showing one example of setting of a correction stepwith respect to a variation of an image enlargement ratio in theimage-shake correcting device shown in FIG. 1;

FIG. 4 is a block diagram showing the arrangement of a video camerawhich is an image pickup apparatus provided with an image-shakecorrecting device according to a second embodiment of the presentinvention;

FIG. 5 is a block diagram showing the arrangement of a video camerawhich is an image pickup apparatus provided with an image-shakecorrecting device according to a third embodiment of the presentinvention;

FIG. 6 is a flowchart showing the control operation of a logic operationcircuit provided in the image-shake correcting device shown in FIG. 5;

FIG. 7 is a flowchart showing in detail the essential processingoperation of the logic operation circuit provided in the image-shakecorrecting device according to the third embodiment;

FIG. 8 is a block diagram showing the arrangement of a video camerawhich is an image pickup apparatus provided with an image-shakecorrecting device according to a fourth embodiment of the presentinvention;

FIG. 9 is a block diagram showing the arrangement of a video camerawhich is an image pickup apparatus provided with an image-shakecorrecting device according to a sixth embodiment of the presentinvention;

FIG. 10 is a flowchart showing the control operation of a logicoperation circuit provided in the image-shake correcting device shown inFIG. 9;

FIG. 11 is a view showing one example of setting of an image enlargementratio for image-shake correction with respect to a variation of a zoommagnification in the image-shake correcting device according to thesixth embodiment;

FIG. 12 is a view showing one example of setting of a correction stepwith respect to a variation of an image enlargement ratio in theimage-shake correcting device according to the sixth embodiment;

FIG. 13 is a block diagram showing the arrangement of a video camerawhich is an image pickup apparatus provided with an image-shakecorrecting device according to a seventh embodiment of the presentinvention;

FIG. 14 is a block diagram showing the arrangement of a video camerawhich is an image pickup apparatus provided with an image-shakecorrecting device according to an eighth embodiment of the presentinvention;

FIG. 15 is a flowchart showing the control operation of a logicoperation circuit provided in the image-shake correcting device shown inFIG. 14;

FIG. 16 is a view showing one example of setting of a correction stepwith respect to a -representative motion vector in the image-shakecorrecting device shown in FIG. 14;

FIG. 17 is a view showing one example of setting of a correction stepwith respect to a representative motion vector in an image-shakecorrecting device according to a ninth embodiment of the presentinvention;

FIG. 18 is a flowchart showing the control operation of a logicoperation circuit provided in an image-shake correcting device accordingto a tenth embodiment of the present invention;

FIG. 19 is a view showing one example of setting of a correction stepwith respect to the amount of displacement of an image in theimage-shake correcting device according to the tenth embodiment;

FIG. 20 is a view showing one example of setting of a correction stepwith respect to the amount of displacement of an image in an image-shakecorrecting device according to an eleventh embodiment; and

FIG. 21 is a block diagram showing the arrangement of a video camerawhich is an image pickup apparatus provided with an image-shakecorrecting device according to a twelfth embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will be described below in detailwith reference to the accompanying drawings.

(First Embodiment)

A first embodiment of the present invention will be described below withreference to FIGS. 1 through 3. FIG. 1 is a block diagram showing thearrangement of a video camera provided with an image-shake correctingdevice according to the first embodiment of the present invention.

The arrangement shown in FIG. 1 includes a focusing lens group 1provided for the purpose of focusing, a zooming lens group 2 foroptically varying a magnification by varying a focal length, acompensation lens group 3 for compensating for a variation of anin-focus position due to a movement of the zooming lens group 2, an iris4 for adjusting the amount of incident light, an image pickup element 5made up of, for example, a two-dimensional CCD provided for converting alight signal inputted through the lens groups 1 to 3 and the iris 4 intoan electrical signal and outputting the electrical signal as a picked-upimage signal, a sample-and-hold (S/H) circuit 6 for sampling and holdingeach pixel of the electrical signal outputted from the image pickupelement 5, and an automatic gain control (AGC) circuit 7 forautomatically controlling the gain of the electrical signal outputtedfrom the S/H circuit 6.

The arrangement shown in FIG. 1 also includes an analog-to-digital (A/D)converter 8 for converting an analog signal outputted from the AGCcircuit 7 into a digital signal, a delay (2HDLY) circuit 9 for receivingthe output signal of the A/D converter 8 and delaying a color-differenceline-sequential signal outputted from the image pickup element 5 by twohorizontal scanning periods (2H), a chrominance signal generating (Cprocess) circuit 10 for receiving the output signal of the 2HDLY circuit9 and generating a chrominance (C) signal, a low-pass filter (LPF) 11for receiving the output signal of the 2HDLY circuit 9 and eliminating achrominance signal C contained in a luminance signal Y, and an enhancer12 for receiving the output signal of the LPF 11 and enhancing ahigh-frequency component.

The arrangement shown in FIG. 1 also includes a gamma (γ) correctioncircuit 13 for receiving the output signal of the enhancer 12 andperforming gamma correction thereof, a two-dimensional band-pass filter(BPF) 14 which is a spatial frequency filter for receiving the outputsignal of the gamma correction circuit 13 and eliminating a signalhaving a predetermined frequency band from the received signal, and amotion-vector detecting circuit 15 for receiving both the output signalof the BPF 14 and the output signal of a first field memory 16 whichindicates an image immediately previous to the current image anddetecting a motion vector of an image on the basis of a correlationbetween both images. The first field memory 16 will be described later.The motion-vector detecting circuit 15 is a circuit which is based on amatching computation, and, in the first embodiment, it is preferablethat the motion-vector detecting circuit 15 adopt a detection methodwhich can execute real-time processing. The first field memory 16 isarranged to receive the output signal of the BPF 14. The first fieldmemory 16 serves as a delay circuit for delaying the luminance signal Yby a predetermined time (in the first embodiment, a one-field period),and is arranged to store the luminance signal Y contained in a fieldwhich immediately precedes the current field, thereby enabling amatching computation on the previous and current fields.

A logic operation circuit 17 controls the entire image pickup apparatusby performing predetermined kinds of signal processing, and is formed bya microcomputer. The logic operation circuit 17 receives the outputsignal of the motion-vector detecting circuit 15 and the output signalof an image-enlargement-ratio input switch (image-enlargement-ratiovarying means) 23 which will be described later. The logic operationcircuit 17 used in the first embodiment has the image-enlargement-ratiovarying means for varying an image enlargement ratio on the basis of theoutput signal of the image-enlargement-ratio input switch 23.

A memory-reading controlling circuit 18 used in the first embodiment isarranged to control the image reading position and area of a secondfield memory 19 (which will be described later) on the basis of acontrol signal outputted from the logic operation circuit 17. Thememory-reading controlling circuit 18 constitutes electronic correctingmeans for correcting an image shake by shifting the image readingposition of the second field memory 19 in the direction of a movement ofan image and cancelling the movement of the image. The second fieldmemory 19 receives the chrominance signal C outputted from the C processcircuit 10 and the luminance signal Y outputted from the gammacorrection circuit 13. In the second field memory 19, the movement ofthe image is corrected for both the chrominance signal C and theluminance signal Y.

An electronic-zoom circuit 20 receives the output signals of the secondfield memory 19 and the logic operation circuit 17 and converts theimage read from the second field memory 19 into an image of desiredsize. Specifically, the electronic-zoom circuit 20 varies an imagereading rate and performs interpolation to electronically enlarge theimage. A digital/analog (D/A) converter 21 is provided for converting adigital signal outputted from the electronic-zoom circuit 20 to ananalog signal. The corrected image signal, which is outputted from theelectronic-zoom circuit 20, is outputted through a signal outputterminal 22. The image-enlargement-ratio input switch 23 is provided forinputting an image enlargement ratio for use in the electronic-zoomcircuit 20, and the output signal of the image-enlargement-ratio inputswitch 23 is inputted to the logic operation circuit 17.

The operation of the image pickup apparatus having the above-describedarrangement will be described below.

An image of a subject 24 sequentially passes through the lens groups 1to 3 and the iris 4 and is formed on an image pickup surface of theimage pickup element 5. The formed image of the subject 24 isphotoelectrically converted by the image pickup element 5. The S/Hcircuit 6 holds the output signal of the image pickup element 5, and theAGC circuit 7 executes automatic gain control. The A/D converter 8performs A/D conversion of the output signal of the AGC circuit 7. The2HDLY circuit 9 separates the color-difference line-sequential signaloutputted from the image pickup element 5 into a 1H delayed signal and a2H delayed signal, and sends the respective 1H and 2H delayed signals toa luminance signal processing part (which includes the LPF 11 and so on)and a chrominance signal processing part (which includes the C processcircuit 10 and so on). The 2H delayed signal sent to the chrominancesignal processing part is inputted to the C process circuit 10, and theC process circuit 10 generates the chrominance signal C and writes thechrominance signal C into the second field memory 19.

In the meantime, the 1H delayed signal sent to the luminance signalprocessing part is inputted to the LPF 11, and the LPF 11 eliminates acarrier component from the color-difference line-sequential signal toperform separation of the luminance-signal Y. The enhancer 12 performsthe processing of enhancing the high-frequency component of theluminance signal Y, such as the edge of the image of the subject 24, forthe purpose of improving image quality. Normally, in such processing, aquadratic differential of the video signal (luminance signal Y) is addedto the original luminance signal Y. Then, the gamma correction circuit13 executes the processing of preventing saturation of the high-lightportion of the luminance signal Y and expanding the dynamic rangethereof. The BPF 14 extracts a spatial frequency component which isuseful for detecting a motion vector.

Since the high- and low-frequency components of an image signal aregenerally unsuitable for detecting a motion vector, they are eliminatedby the BPF 14. In the first embodiment, only a sign bit is outputtedfrom the BPF 14. This means that the luminance signal Y is convertedinto a two-level signal by using a DC level as a threshold. Accordingly,the luminance signal Y which has passed through the BPF 14 is atwo-level signal represented by one bit.

The motion-vector detecting circuit 15 detects a motion vector of theimage on the basis of the signals inputted from the BPF 14 and the firstfield memory 16, and inputs the detected motion vector signal to thelogic operation circuit 17. Also, an enlargement-ratio signal indicativeof an image enlargement ratio to be used during image-shake correctionis inputted from the image-enlargement-ratio input switch 23 to thelogic operation circuit 17. The logic operation circuit 17 calculates adeviation from a reference position of the image at that time instant inaccordance with the flowchart shown in FIG. 2 which will be describedlater, on the basis of the motion vector signal (the horizontal andvertical components of a motion vector at a predetermined position inthe picture). Then, the memory-reading controlling circuit 18 controlsthe image reading position of the second field memory 19 with acorrection step according to the image enlargement ratio, and the imageoutputted from the second field memory 19 is converted into an image ofdesired size by the electronic-zoom circuit 20. In this manner, theimage whose image shake is finally corrected is obtained. The correctedimage signal is D/A converted by the D/A converter 21, and the analogsignal is outputted through the signal output terminal 22.

The operation of the logic operation circuit 17 provided in theimage-shake correcting device according to the first embodiment will bedescribed below with reference to FIGS. 1 and 2. FIG. 2 is a flowchartshowing the operation of the logic operation circuit 17. In Step S201,the logic operation circuit 17 reads the output signal of themotion-vector detecting circuit 15 (the horizontal and verticalcomponents of a motion vector at a predetermined position in a picture)on field-by-field basis. Then, the process proceeds to Step S202, inwhich the logic operation circuit 17 detects movement of an image in theread plurality of pictures at a plurality of positions per picture andperforms predetermined processing on motion vectors at the plurality ofpositions, thereby computing one representative motion vector. Thepredetermined processing includes the process of performing averaging,such as the process of evaluating the reliability of each of the motionvectors or the processing of determining a target area to be controlled.

Then, the process proceeds to Step S203, in which the logic operationcircuit 17 integrates the representative motion vector to find adeviation from a reference position in the picture (the amount ofdisplacement of the image), thereby producing an image-shake correctionsignal. Then, the process proceeds to Step S204, in which the logicoperation circuit 17 reads an enlargement-ratio signal outputted fromthe image-enlargement-ratio input switch 23 and controls theelectronic-zoom circuit 20 so that a desired enlargement ratio can beobtained. Then, the process proceeds to Step S205, in which the logicoperation circuit 17 sets the correction step of the memory-readingcontrolling circuit 18 to an optimum state on the basis of the imageenlargement ratio set in Step S204. Then, the process proceeds to StepS206, in which the image shake is corrected by moving the image readingposition of the second field memory 19 with the image enlargement ratioset in Step S204 and the correction step set in Step S205. After that,the logic operation circuit 17 brings the process to an end.

The processing routines of Step S204 and Step S205, which constitutepart of the gist of the present invention, will be described in moredetail with reference to FIGS. 1 and 3.

FIG. 3 is a view showing one example of setting of the correction stepwith respect to a variation of the image enlargement ratio. In FIG. 3,the vertical and horizontal axes represent the correction step and theimage enlargement ratio, respectively. In FIG. 3, normally, thecorrection step is set according to the accuracy of detection of animage shake. The image enlargement ratio indicates an image enlargementratio for image-shake correction, which is arbitrarily inputted throughthe image-enlargement-ratio input switch 23 by a photographer and is setin Step S204 of FIG. 2.

In general, as the image enlargement ratio is made larger, a correctionrange becomes wider and the frequency of occurrence of a resolutiondegradation becomes higher. Specifically, if the image enlargement ratiois made larger, an image reading area of a memory can be made smaller,so that it is possible to enlarge the amount by which the image readingarea can be shifted on the memory. In consequence, the amount of shakecorrection becomes large, but since pixel information is lost, aresolution degradation becomes large. Contrarily, as the imageenlargement ratio is made smaller, the correction range becomes narrowerand the frequency of occurrence of a resolution degradation becomeslower. Accordingly, if, for example, a photographer determines thatthere is no large image shake or desires to avoid a degradation inresolution, the photographer may set the image enlargement ratio to asmall value. If, for example, the photographer determines that there isa large image shake, the photographer intentionally sets the imageenlargement ratio to a large value, whereby it is possible to correct animage shake which is normally impossible to correct.

However, it has been found out that as the correction step is madesmaller, a movement of a position at which a resolution degradationoccurs due to image enlargement processing becomes more noticeable. Theextent of this movement greatly varies with the image enlargement ratio,and most greatly varies at an image enlargement ratio of approximately1.1× in terms of visual characteristics. If the image enlargement ratiois smaller or larger than approximately 1.1×, the resolution degradationbecomes unnoticeable. For this reason, as shown in FIG. 3, if thecorrection step is set to a value at which the resolution degradation ismost unnoticeable, according to the image enlargement ratio set by thephotographer, a satisfactory image can be obtained under anyphotographic condition. Accordingly, in the example shown in FIG. 3, thecorrection step is made large at the image enlargement ratio ofapproximately 1.1× at which the resolution degradation is mostnoticeable, whereas the correction step is made small in a zone of imageenlargement ratio lower than approximately 1.1× as well as a zone ofimage enlargement ratio higher than approximately 1.1×.

According to the first embodiment, there is provided an image-shakecorrecting device capable of electronically correcting an image shake,which allows a photographer to arbitrarily vary an image enlargementratio to be used during image-shake correction, under variousphotographic conditions. In addition, in the image-shake correctingdevice, since the correction step with which an image shake is correctedcan be set to an optimum state according to the image enlargement ratio,it is possible to minimize a resolution degradation and noise due to amovement of the position of occurrence of the resolution degradation.Accordingly, it is possible to achieve the advantage of minimizing animage degradation due to image-shake correction.

(Second Embodiment)

A second embodiment of the present invention will be described belowwith reference to FIG. 4.

FIG. 4 is a block diagram showing the arrangement of a video cameraprovided with an image-shake correcting device according to the secondembodiment of the present invention. In FIG. 4, identical referencenumerals are used to denote constituent parts identical to those used inthe above-described first embodiment. The arrangement shown in FIG. 4differs from that shown in FIG. 1 in that the image pickup element 5,the memory-reading controlling circuit 18 and the second field memory 19are omitted from the arrangement shown in FIG. 4 and, instead, alarge-area image pickup element 5′, having a larger area than a normalimage pickup element, and an image-pickup-element reading circuit 25 areprovided. The large-area image pickup element 5′ and theimage-pickup-element reading circuit 25 constitute correcting meanswhich has a feedback loop and serves to correct an image shake. Theimage-pickup-element reading circuit 25 varies the reading address ofthe large-area image pickup element 5′ to cut out an image from anarbitrary area of the large-area image pickup element 5′ and shift theposition of the cut-out image, thereby effecting image-shake correction.

The other arrangement, operation, effects and advantages of the secondembodiment are substantially identical to those of the first embodimentdescribed previously, and description thereof is omitted.

(Third Embodiment)

The third embodiment of the present invention will be described belowwith reference to FIGS. 5 through 7. FIG. 5 is a block diagram showingthe arrangement of a video camera provided with an image-shakecorrecting device according to the third embodiment of the presentinvention. In FIG. 5, identical reference numerals are used to denoteconstituent parts identical to those used in the first embodimentdescribed above with reference to FIG. 1. The arrangement shown in FIG.5 differs from that shown in FIG. 1 in that the image-enlargement-ratioinput switch 23 is omitted from the arrangement shown in FIG. 1 and,instead, a tripod-mounting detection signal generating circuit 26 forgenerating a tripod-mounting detection signal indicating that the videocamera is supported on a supporting stand (tripod) is added to thearrangement shown in FIG. 1. The tripod-mounting detection signalgenerating circuit 26 includes constituent elements (not shown), such asa switch for generating a detection signal when a mounting screw of atripod is screwed into a threaded hole formed in a tripod mountingportion of the video camera. In the third embodiment, the logicoperation circuit 17 constitutes support detecting means for detectingwhether the video camera is supported on the tripod on the basis of thetripod-mounting detection signal generated by the tripod-mountingdetection signal generating circuit 26.

The construction and operation of the other portion of the thirdembodiment are substantially identical to the construction and operationof the first embodiment described previously, and description thereof isomitted.

The operation of the logic operation circuit 17 provided in theimage-shake correcting device according to the third embodiment will bedescribed below with reference to FIGS. 5 and 6. FIG. 6 is a flowchartshowing the operation of the logic operation circuit 17. In Step S601,the logic operation circuit 17 reads the output signal of themotion-vector detecting circuit 15 (the horizontal and verticalcomponents of a motion vector at a predetermined position in a picture)on field-by-field basis. Then, the process proceeds to Step S602, inwhich the logic operation circuit 17 performs predetermined processingon the read plurality of motion vectors at positions in a plurality offields, thereby computing one representative motion vector. Thepredetermined process includes the processing of evaluating thereliability of each of the motion vectors, the process of determining atarget area to be controlled, and the like.

Then, the process proceeds to Step S603, in which the logic operationcircuit 17 integrates the representative motion vector to find adeviation from a reference position in the picture (the amount ofdisplacement of the image), thereby producing an image-shake correctionsignal. Then, the process proceeds to Step S604, in which the logicoperation circuit 17 reads a detection signal outputted from thetripod-mounting detection signal generating circuit 26 and sets both animage enlargement ratio and a correction step of the memory-readingcontrolling circuit 18 to their respective optimum states on the basisof the detection signal. Then, the process proceeds to Step S605, inwhich the image shake is corrected by moving the image on the basis ofthe image enlargement ratio and the correction step which have been setin Step S604. After that, the logic operation circuit 17 brings theprocess to an end.

The processing of Step S604 of FIG. 6, which constitutes part of thegist of the present invention, will. be described in more detail withreference to FIGS. 5 and 7. FIG. 7 is a flowchart showing the detail ofthe processing routine of Steps S604 and S605 of FIG. 6. In Step S701 ofFIG. 7, the logic operation circuit 17 receives the detection signaloutputted from the tripod-mounting detection signal generating circuit26, and, in Step S702, determines whether the video camera is mounted ona tripod on the basis of the detection signal obtained in Step S701. Ifit is determined that the video camera is mounted on the tripod, theprocess proceeds to Step S703, in which the image enlargement ratio isset to 1×. Then, in Step S704, the correction step is set to a minimum.If it is not determined in Step S702 that the video camera is mounted onthe tripod, the process proceeds to Step S705, in which the imageenlargement ratio is set to 1.2×. Then, in Step S704, the correctionstep is set to a maximum.

In general, during photography with a video camera mounted on a tripod,since the amplitude of an image shake is small, it is possible toperform image-shake correction based on only field memory control whichdoes not involve electronic enlargement processing using theelectronic-zoom circuit 20. However, in this case, since an image isstable so that a movement of the image tends to be considerablynoticeable during shifting thereof, the correcting step is made small sothat the image can be smoothly moved. During photography with the videocamera removed from the tripod, since the amplitude of an image shake islarge, the electronic enlargement processing using the electronic-zoomcircuit 20 is performed to assure a correction range, and the correctionstep is set large to make a movement of a position of occurrence of aresolution degradation as unnoticeable as possible.

As described above, according to the third embodiment, in an image-shakecorrecting device capable of electronically correcting an image shake,it is determined whether the video camera is mounted on the tripod, andan optimum image enlargement ratio-and a correction step (shifting step)with which an image is moved are set on the basis of the decisionresult. Accordingly, it is possible to minimize a resolution degradationand a noise due to a movement of the position of occurrence of theresolution degradation, whereby it is possible to achieve the advantageof minimizing an image degradation due to image-shake correction.

(Fourth Embodiment)

A fourth embodiment of the present invention will be described belowwith reference to FIG. 8.

FIG. 8 is a block diagram showing the arrangement of a video cameraprovided with an image-shake correcting device according to the fourthembodiment of the present invention. In FIG. 8, identical referencenumerals are used to denote constituent parts identical to those used inthe above-described third embodiment shown in FIG. 5. The arrangementshown in FIG. 8 differs from that shown in Figure in that the imagepickup element 5, the memory-reading controlling circuit 18 and thesecond field memory 19 are omitted from the arrangement shown in FIG. 5and, instead, a large-area image pickup element 5′, having a larger areathan a normal image pickup element, and an image-pickup-element readingcircuit 25 are provided. The large-area image pickup element 5′ and theimage-pickup-element reading circuit 25 constitute first correctingmeans which has a feedback loop and serves to correct an image shake.The image-pickup-element reading circuit 25 varies the reading addressof the large-area image pickup element 5′ to cut out an image from anarbitrary area of the large-area image pickup element 5′, therebyeffecting image-shake correction.

The other arrangement, operation, effects and advantages of the fourthembodiment are substantially identical to those of the third embodimentdescribed previously, and description thereof is omitted.

(Fifth Embodiment)

Each of the third and fourth embodiments is arranged in such a mannerthat when the mounting screw of a tripod is screwed into the threadedhole of the tripod mounting portion of the video camera, thetripod-mounting detection signal generating circuit 26 generates adetection signal which indicates that the video camera has been mountedon the tripod. However, the present invention is not limited to such anarrangement, and it is also possible to adopt, for example, anarrangement which determines whether the video camera is mounted on thetripod, from the state of distribution of motion vectors. In thisarrangement, if, for example, the motion vectors continue to be notgreater than a predetermined value as a whole for a predetermined timeperiod, it is determined that the video camera has been mounted on thetripod.

(Sixth embodiment)

The sixth embodiment of the present invention will be described belowwith reference to FIGS. 9 through 12.

FIG. 9 is a block diagram showing the arrangement of a video cameraprovided with an image-shake correcting device according to the sixthembodiment of the present invention. In FIG. 9, identical referencenumerals are used to denote constituent parts identical to those used inthe first embodiment described above with reference to FIG. 1. Thearrangement shown in FIG. 9 differs from that shown in FIG. 1 in thatthe image-enlargement-ratio input switch 23 is omitted from thearrangement shown in FIG. 1 and, instead, a zoom encoder 27 fordetecting the position of the zooming lens group 2 is provided. Aposition signal about the zooming lens group 2, which is detected by thezoom encoder 27, is inputted to the logic operation circuit 17.Incidentally, the other arrangement, operation, effects and advantagesof the sixth embodiment are substantially identical to those of thefirst embodiment described previously, and description thereof isomitted.

The operation of the logic operation circuit 17 used in the image-shakecorrecting device according to the sixth embodiment will be describedbelow with reference to FIGS. 9 and 10. FIG. 10 is a flowchart showingthe operation of the logic operation circuit 17. In Step S1001, thelogic operation circuit 17 reads the output signal of the motion-vectordetecting circuit 15 (the horizontal and vertical components of a motionvector at a predetermined position in a picture) on field-by-fieldbasis. Then, the process proceeds to Step S1002, in which the logicoperation circuit 17 performs predetermined processing on the readplurality of motion vectors at positions in a plurality of fields,thereby computing one representative motion vector. The predeterminedprocess includes the processing of evaluating the reliability of each ofthe motion vectors, the process of determining a target area to becontrolled, and the like.

Then, the process proceeds to Step S1003, in which the logic operationcircuit 17 integrates the representative motion vector to find adeviation from a reference position in the picture (the amount ofdisplacement-of the image), thereby producing an image-shake correctionsignal. Then, the process proceeds to Step S1004, in which the logicoperation circuit 17 sets an optimum image enlargement ratio forimage-shake correction on the basis of a focal-length signal about anoptical system which is outputted from the zoom encoder 27 and anelectronic-zoom magnification signal which is outputted from theelectronic-zoom circuit 20. Then, the process proceeds to Step S1005, inwhich the correction step of the memory-reading controlling circuit 18is set to an optimum state according to the image enlargement ratio setin Step S1004. Then, the process proceeds to Step S1005, in which theimage shake is corrected by moving the image on the basis of the imageenlargement ratio set in Step S1004 and the correction step set in StepS1005. After that, the logic operation circuit 17 brings the process toan end.

The processing routines of Steps S1004 and 1005 of FIG. 10, whichconstitute part of the gist of the present invention, will be describedin more detail with reference to FIGS. 10, 11 and 12.

FIG. 11 is a view showing one example of setting of the imageenlargement ratio for image-shake correction with respect to a variationof a zoom magnification. In FIG. 11, the vertical and horizontal axesrepresent the image enlargement ratio and the zoom magnification,respectively. The zoom magnification is a magnification which is set bya photographer manipulating a zoom magnification setting switch (notshown), and if there are an optical-zoom zone and an electronic-zoomzone, as in the case of the sixth embodiment, the zoom magnificationwill be a magnification obtained by multiplying an optical-zoommagnification by an electronic-zoom magnification.

In general, if image-shake correction is to be electronically performed,it is necessary to enlarge an image to gain a correction range. Inprinciple, as the image enlargement ratio is made larger, the correctionrange becomes wider. However, it is well known that even a small extentof image enlargement brings about a degradation in image quality. Inaddition, the amplitude of an image shake greatly depends on the zoommagnification and becomes smaller toward a wide-angle end. Accordingly,in Step S1004 of FIG. 10, if image-shake correction is performed at animage enlargement ratio of 1×, as shown in FIG. 11, without enlarging animage on a wide-angle side of the optical-zoom zone, the frequency ofoccurrence of resolution degradation is reduced.

FIG. 12 is a view showing one example of setting of the correction stepwith respect to a variation of the image enlargement ratio. In FIG. 12,the vertical and horizontal axes represent the correction step and theimage enlargement ratio, respectively. The correction step is theminimum unit in which an image is shifted, and is normally set accordingto the accuracy of detection of an image shake. However, it has beenfound out that as the correction step is made smaller, a movement of aposition at which a resolution degradation occurs due to imageenlargement processing becomes more noticeable. Since such a movement isnot similarly noticeable at all image enlargement ratios, it is possibleto reduce a moiré noise by increasing a correction step at an imageenlargement ratio of approximately 1.1× at which the movement is mostnoticeable, as shown in FIG. 12.

(Seventh Embodiment)

A seventh embodiment of the present invention will be described belowwith reference to FIG. 13.

FIG. 13 is a block diagram showing the arrangement of a video cameraprovided with an image-shake correcting device according to the seventhembodiment of the present invention. In FIG. 13, identical referencenumerals are used to denote constituent parts identical to those used inthe above-described sixth embodiment shown in FIG. 9. The arrangementshown in FIG. 13 differs from that shown in FIG. 9 in that the imagepickup element 5, the memory-reading controlling circuit 18 and thesecond field memory 19 are omitted from the arrangement shown in FIG. 9and, instead, the large-area image pickup element 5′, having a largerarea than a normal image pickup element, and the image-pickup-elementreading circuit 25 are provided. The large-area image pickup element 5′and the image-pickup-element reading circuit 25 constitute firstcorrecting means which has a feedback loop and serves to correct animage shake. The image-pickup-element reading circuit 25 varies thereading address of the large-area image pickup element 5′ to cut out animage from an arbitrary area of the large-area image pickup element 5′,thereby effecting image-shake correction.

The other arrangement, operation, effects and advantages of the seventhembodiment are substantially identical to those of the sixth embodimentdescribed previously, and description thereof is omitted.

As is apparent from the above detailed description, in accordance witheach of the first to seventh embodiments, there is provided animage-shake correcting device capable of electronically correcting animage shake, which allows a photographer to arbitrarily vary an imageenlargement ratio to be used during image-shake correction. In addition,in the image-shake correcting device, since the correction step withwhich an image shake is corrected can be set to an optimum stateaccording to the image enlargement ratio, it is possible to minimize aresolution degradation and noise due to a movement of the position ofoccurrence of the resolution degradation. Accordingly, it is possible toachieve the advantage of minimizing an image degradation due toimage-shake correction.

Eighth to twelfth embodiments of the present invention will be describedbelow.

According to the eighth to twelfth embodiments, there is provided animage-shake correcting device which includes motion-vector detectingmeans for detecting a motion vector relative to images, electroniccorrecting means for electronically correcting an image shake on thebasis of the motion vector detected by the motion-vector detectingmeans, and control means for controlling both a correction step and animage enlargement ratio of the electronic correcting means on the basisof the value of the motion vector to set the correction step and theimage enlargement ratio to their respective optimum states.

According to the eighth to twelfth embodiments, there is provided animage-shake correcting device which includes motion-vector detectingmeans for detecting a motion vector relative to images,absolute-deviation computing means for computing an absolute deviationfrom a reference point of a current image on the basis of the motionvector detected by the motion-vector detecting means, electroniccorrecting means for electronically correcting an image shake on thebasis of the absolute deviation computed by the absolute-deviationcomputing means, and control means for controlling both a correctionstep and an image enlargement ratio of the electronic correcting meanson the basis of the absolute deviation to set the correction step andthe image enlargement ratio to their respective optimum states.

(Eighth Embodiment)

In FIG. 14 which shows the eighth embodiment of the present invention,identical reference numeral are used to denote constituent partsidentical to those of the first embodiment shown in FIG. 1, anddescription thereof is omitted. In the eighth embodiment, theimage-enlargement-ratio input switch 23 is omitted from the arrangementshown in FIG. 1, and a logic operation circuit 117 has a processingprogram different from that of the logic operation circuit 17 shown inFIG. 1.

The logic operation circuit 117 performs the operation of controlling,on the basis a motion vector outputted from the motion-vector detectingcircuit 15, the operation of the memory-reading controlling circuit 18in the direction of the motion vector, shifting an image readingposition of the second field memory 19 from which an image is to be readout, and correcting a movement of the image. The logic operation circuit117 also performs the operation of executing optimum control of thecorrection step of the memory-reading controlling circuit 18 and theimage enlargement ratio of the electronic-zoom circuit 20 in accordancewith the magnitude of the motion vector.

The operation of the image pickup apparatus having the above-describedarrangement will be described below.

An image of the subject 24 sequentially passes through the lens groups 1to 3 and the iris 4 and is formed on the image pickup surface of theimage pickup element 5. The formed image of the subject 24 isphotoelectrically converted by the image pickup element 5. The S/Hcircuit 6 holds the output signal of the image pickup element 5, and theAGC circuit 7 executes automatic gain control. The A/D converter 8performs A/D conversion of the output signal of the AGC circuit 7. The2HDLY circuit 9 separates the color-difference line-sequential signaloutputted from the image pickup element 5 into a 1H delayed signal and a2H delayed signal, and sends the respective 1H and 2H delayed signals tothe luminance signal processing part (which includes the LPF 11 and soon) and the chrominance signal processing part (which includes the Cprocess circuit 10 and so on). The 2H delayed signal sent to thechrominance signal processing part is inputted to the C process circuit10, and the C process circuit 10 generates the chrominance signal C andwrites the chrominance signal C into the second field memory 19.

In the meantime, the 1H delayed signal sent to the luminance signalprocessing part is inputted to the LPF 11, and the LPF 11 eliminates acarrier component from the color-difference line-sequential signal toperform separation of the luminance signal Y. The enhancer 12 performsthe processing of enhancing the high-frequency component of theluminance signal Y, such as the edge of the image of the subject 24, forthe purpose of improving image quality. Normally, in such processing, aquadratic differential of the video signal (luminance signal Y) is addedto the original luminance signal Y. Then, the gamma correction circuit13 executes the processing of preventing saturation of the high-lightportion of the luminance signal Y and expanding the dynamic rangethereof. The BPF 14 extracts a spatial frequency component which isuseful for detecting a motion vector.

Since the high- and low-frequency components of an image signal aregenerally unsuitable for detecting a motion vector, they are eliminatedby the BPF 14. In the eighth embodiment, only a sign bit is outputtedfrom the BPF 14. This means that the luminance signal Y is convertedinto a two-level signal by using a DC level as a threshold. Accordingly,the luminance signal Y which has passed through the BPF 14 is atwo-level signal represented by one bit.

The motion-vector detecting circuit 15 detects a motion vector of theimage on the basis of the signals inputted from the BPF 14 and the firstfield memory 16, and inputs the detected motion vector signal to thelogic operation circuit 117. The logic operation circuit 117 calculatesa deviation from a reference position of the image at that time instantin accordance with the flowchart shown in FIG. 15 which will bedescribed later, on the basis of the motion vector signal (thehorizontal and vertical components of a motion vector at a predeterminedposition in the picture). Then, the memory-reading controlling circuit18 controls the image reading position of the second field memory 19with a correction step according to the image enlargement ratio, and theimage outputted from the second field memory 19 is enlarged at apredetermined image enlargement ratio by the electronic-zoom circuit 20.In this manner, the image whose image shake is finally corrected isobtained. The corrected image signal is D/A converted by the D/Aconverter 21, and the analog signal is outputted through the signaloutput terminal 22.

The operation of the logic operation circuit 117 provided in theimage-shake correcting device according to the eighth embodiment will bedescribed below with reference to FIGS. 14 and 15. FIG. 15 is aflowchart showing the operation of the logic operation circuit 117. InStep S1501 of FIG. 15, the logic operation circuit 117 reads the outputsignal of the motion-vector detecting circuit 15 (the horizontal andvertical components of a motion vector at a predetermined position in apicture) on field-by-field basis. Then, the process proceeds to StepS1502, in which the logic operation circuit 117 detects a movement of animage in the plurality of pictures read in Step S1501 at a plurality ofpositions per picture and performs predetermined processing on motionvectors at the plurality of positions, thereby computing onerepresentative motion vector. The predetermined processing includes theprocessing of evaluating the reliability of each of the motion vectors,the process of determining a target area to be controlled, averagingprocess and the like.

Then, the process proceeds to Step S1503, in which the logic operationcircuit 117 integrates the representative motion vector to find adeviation from a reference position in the picture (the amount ofdisplacement of the image), thereby producing an image-shake correctionsignal. Then, the process proceeds to Step S1504, in which the logicoperation circuit 117 sets the correction step of the memory-readingcontrolling circuit 18 to an optimum state according to an absolutevalue of the representative motion vector computed in Step S1502. Then,the process proceeds to Step S1505, in which image-shake correction isexecuted by moving the image with the correction step set in Step S1504.After that, the logic operation circuit 117 brings the process to anend.

The processing routines of Step S1504 of FIG. 15, which constitute partof the gist of the present invention, will be described in more detailwith reference to FIGS. 14 and 16.

FIG. 16 is a view showing the relation between the representative motionvector and a correction step optimum therefor. In FIG. 16, the verticaland horizontal axes represent the correction step and the representativemotion vector, respectively. In FIG. 16, the representative motionvector represents the relative displacement between a current image andan image which immediately precedes the current image. The correctionstep is the minimum unit in which an image is shifted, and is normallyset according to the accuracy of detection of a motion vector. However,it has been found out that as the correction step is made smaller tomove an image in finer steps, a movement of a position at which aresolution degradation occurs due to image enlargement processingbecomes more noticeable.

As shown in FIG. 16, as the representative motion vector has a largermagnitude, i.e., an image shake becomes larger, the degree of finenessto which an image is corrected becomes less significant. Accordingly, asthe magnitude of the representative motion vector becomes larger, thecorrection step is made larger to make the movement of the position ofoccurrence of the resolution degradation less noticeable. Contrarily, asthe representative motion vector has a smaller magnitude, i.e., theimage shake becomes smaller, the awkwardness with which the image iscorrected becomes more noticeable. Accordingly, as the magnitude of therepresentative motion vector becomes smaller, the correction step ismade smaller so that it is possible to reduce a resolution degradationas well as a noise due to a movement of a position at which theresolution degradation occurs.

According to the eighth embodiment, there is provided an image-shakecorrecting device capable of electronically correcting an image shake,in which, since the correction step (shifting step) with which the imageshake is corrected can be set to an optimum state according to theabsolute value of a representative motion vector, i.e., the degree ofthe image shake, it is possible to minimize a resolution degradation anda noise due to a movement of a position at which the resolutiondegradation occurs. Accordingly, it is possible to achieve the advantageof minimizing an image degradation due to image-shake correction.

(Ninth Embodiment)

The ninth embodiment of the present invention will be described belowwith reference to FIG. 17. FIG. 17 is a view showing the relationbetween a representative motion vector and a correction step optimumtherefor in an image-shake correcting device according to the ninthembodiment. In the ninth embodiment, the relation between therepresentative motion vector and the correction step optimum therefor ismade to vary not stepwise as in the case of the eighth embodiment but ina manner expressed by an exponential function. It is possible,therefore, to achieve a smoother variation of such relation.

Incidentally, the other arrangement, operation, effects and advantagesof the ninth embodiment are substantially identical to those of theeighth embodiment described previously, and description thereof isomitted.

(Tenth Embodiment)

The tenth embodiment of the present invention will be described belowwith reference to FIGS. 18 and 19. The arrangement of a video camerawhich is an image pickup apparatus provided with an image-shakecorrecting device according to the tenth embodiment of the presentinvention is substantially identical to that of the previously-describedeighth embodiment shown in FIG. 14, and the following description willbe made with reference to FIG. 14 as well. FIG. 18 is a flowchartshowing the operation of the logic operation circuit 117 provided in theimage-shake correcting device according to the tenth embodiment. In StepS1801 of FIG. 18, the logic operation circuit 117 reads the outputsignal of the motion-vector detecting circuit 15 (the horizontal andvertical components of a motion vector at a predetermined position in apicture) on field-by-field basis. Then, the process proceeds to StepS1802, in which the logic operation circuit 117 performs predeterminedprocessing on the read plurality of motion vectors at positions in aplurality of fields, thereby computing one representative motion vector.The predetermined processing includes the process of evaluating thereliability of each of the motion vectors, the process of determining atarget area to be controlled, and the like.

Then, the process proceeds to Step S1803, in which the logic operationcircuit 117 integrates the representative motion vector to find adeviation from a reference position in the picture (the amount ofdisplacement of the image), thereby producing an image-shake correctionsignal. Then, the process proceeds to Step S1804, in which the logicoperation circuit 117 sets the correction step of the memory-readingcontrolling circuit 18 to an optimum state on the basis of an absolutevalue of the deviation of the image calculated in Step S1803. Then, theprocess proceeds to Step S1805, in which image-shake correction isexecuted by moving the image with the correction step set in Step S1804.After that, the logic operation circuit 117 brings the process to anend.

The processing of Step S1804, which constitutes part of the gist of thepresent invention, will be described in more detail with reference toFIGS. 14 and 19.

FIG. 19 is a view showing the relation between the amount ofdisplacement of the image and a correction step optimum therefor. InFIG. 19, the vertical axis and the horizontal axis represent thecorrection step and the amount of displacement of the image,respectively. The amount of displacement of the image represents therelative position of the current image with respect to a predeterminedreference position. The correction step is the minimum unit in which animage is shifted, and is normally set according to the accuracy ofdetection of a motion vector. However, it has been found out that as thecorrection step is made smaller to move an image in finer steps, amovement of a position at which a resolution degradation occurs due toimage enlargement processing becomes more noticeable.

As shown in FIG. 19, as the representative motion vector has a largermagnitude, i.e., an image shake becomes larger, the degree of finenessto which an image is corrected becomes less significant. Accordingly, asthe magnitude of the representative motion vector becomes larger, thecorrection step is made larger to make the movement of the position ofoccurrence of the resolution degradation less noticeable. Contrarily, asthe representative motion vector has a smaller magnitude, i.e., theimage shake becomes smaller, the awkwardness with which the image iscorrected becomes more noticeable. Accordingly, as the magnitude of therepresentative motion vector becomes smaller, the correction step ismade smaller so that it is possible to reduce a resolution degradationas well as a noise due to a movement of a position at which theresolution degradation occurs.

According to the tenth embodiment, there is provided an image-shakecorrecting device capable of electronically correcting an image shake,in which since the correction step with which the image shake iscorrected can be set to an optimum state according to the amount ofdisplacement of an image, i.e., the degree of the image shake, it ispossible to minimize a resolution degradation and a noise due to amovement of a position at which the resolution degradation occurs.Accordingly, it is possible to achieve the advantage of minimizing animage degradation due to image-shake correction.

(Eleventh Embodiment)

The eleventh embodiment of the present invention will be described belowwith reference to FIG. 20. FIG. 20 is a view showing the relationbetween the amount of displacement of an image and a correction stepoptimum therefor in an image-shake correcting device according to theeleventh embodiment. In the eleventh embodiment, the relation betweenthe amount of displacement of the image and the correction step optimumtherefor is made to vary not stepwise, as in the case of the tenthembodiment, but in a manner expressed by an exponential function. It ispossible, therefore, to achieve a smoother variation of such relation.

Incidentally, the other arrangement, operation, effects and advantagesof the ninth embodiment are substantially identical to those of thetenth embodiment described previously, and description thereof isomitted.

(Twelfth Embodiment)

Although the description of each of the eight to eleventh embodimentshas referred to the image-shake correcting device arranged to performimage-shake correction by using a field memory, the present invention isnot limited to such an arrangement. For example, the present inventioncan be applied to an image-shake correcting device which is arranged toperform image-shake correction by using, instead of the field memory, alarge-area image pickup element having a larger area than a normal imagepickup element.

FIG. 21 is a block diagram showing the arrangement of a video cameraprovided with an image-shake correcting device according to the twelfthembodiment of the present invention. In FIG. 21, identical referencenumerals are used to denote constituent parts identical to those used inthe above-described eighth embodiment shown in FIG. 14. The arrangementshown in FIG. 21 differs from that shown in FIG. 14 in that the imagepickup element 5, the memory-reading controlling circuit 18 and thesecond field memory 19 are omitted from the arrangement shown in FIG. 14and, instead, the large-area image pickup element 5′ having a largerarea than a normal image pickup element and the image-pickup-elementreading circuit 25 are provided. The large-area image pickup element 5′and the image-pickup-element reading circuit 25 constitute correctingmeans which has a feedback loop and serves to correct an image shake.The image-pickup-element reading circuit 25 varies the reading addressof the large-area image pickup element 5′ to cut out an image from anarbitrary area of the large-area image pickup element 5′, therebyeffecting image-shake correction.

As is apparent from the foregoing detailed description, according toeach of the above-described embodiments, there is provided animage-shake correcting device capable of electronically correcting animage shake, in which since the correction step with which the imageshake is corrected can be set. to an optimum state according to thedegree of the image shake, it is possible to minimize a resolutiondegradation and a noise due to a movement of a position at which theresolution degradation occurs. Accordingly, it is possible to achievethe advantage of minimizing an image degradation due to image-shakecorrection.

What is claimed is:
 1. An image-shake correcting device comprising: (a)motion-vector detecting means for detecting a motion vector; (b)electronic correcting means for electronically correcting image shake ofan image by a predetermined correction step by unit on the basis of anoutput of said motion-vector detecting means; and (c) control means forchanging a unit value of the predetermined correction step of saidelectronic correcting means on the basis of a magnitude of the motionvector detected by said motion-vector detecting means.
 2. An image-shakecorrecting device according to claim 1, further comprising image pickupmeans, said motion-vector detecting means detecting a motion vector ofan image from a pickup image signal output from said image pickup means.3. An image-shake correcting device according to claim 1, wherein saidelectronic correcting means has an image memory for storing the imageand corrects image shake by shifting an image reading position of saidimage memory in a direction of the motion vector output from saidmotion-vector detecting means.
 4. An image-shake correcting deviceaccording to claim 3, wherein said electronic correcting means includescomputing means for computing an absolute deviation from a referenceposition of the image on the basis of the motion vector detected by saidmotion-vector detecting means, and corrects image shake by shifting theimage reading position of said image memory on the basis of the absolutedeviation.
 5. An image-shake correcting device according to claim 1,wherein said control means makes the unit of the correction step of saidelectronic correcting means larger if the motion vector is larger,whereas if the motion vector is smaller, said control means makes theunit of the correction step of said electronic correcting means smaller.6. An image-shake correcting device according to claim 5, wherein saidcontrol means varies the unit of the correction step in a mannerrepresented by an exponential function.
 7. An image-shake correctingdevice comprising: (a) motion-vector detecting means for detecting amotion vector; (b) electronic correcting means, having an image memoryfor storing an image, and arranged for correcting image shake byshifting an image reading position of said image memory by apredetermined step by unit in a direction of the motion vector outputfrom said motion-vector detecting means; and (c) control means forchanging a unit value of the predetermined step of said electroniccorrecting means on the basis of a magnitude of the motion vectordetected by said motion-vector detecting means.
 8. An image-shakecorrecting device according to claim 7, further comprising image pickupmeans, said motion-vector detecting means detecting a motion vector ofthe image from a pickup image signal output from said image pickupmeans.
 9. An image-shake correcting device according to claim 8, whereinsaid electronic correcting means includes computing means for computingan absolute deviation from a reference position of the image on thebasis of the motion vector detected by said motion-vector detectingmeans, and corrects image shake by shifting the image reading positionof said image memory on the basis of the absolute deviation.
 10. Animage-shake correcting device according to claim 9, wherein said controlmeans makes the unit of the correction step of said electroniccorrecting means smaller if the absolute deviation is smaller, whereasif the absolute deviation is larger, said control means makes the unitof the correction step of said electronic correcting means larger. 11.An image-shake correcting device according to claim 10, wherein saidcontrol means varies the unit of the correction step in a mannerrepresented by an exponential function.